(a) Field of the Invention
The present invention relates to a system and a method for measuring current in a high voltage transmission line and transmitting the measured values by fiber optics. Particularly, but not exclusively, the measuring may be effected on a continuing basis and at high frequencies.
(b) Statement of the Prior Art
Because of increasing requirements for higher voltages, the transformers used in transmission lines are becoming larger and larger and more expensive to fabricate and install. Furthermore, existing test apparatus are not well isolated from radio frequency interference and thus subjected to noise and are not readily adaptable to computer or microprocessor-type measuring apparatus which are becoming more and more prevalent.
There is, therefore, a need to use more advanced technology in high voltage transmission systems and the present invention is concerned with the utilization of optical fibers to carry transmitted information from a sensor circuit located on a high voltage line. An advantage of using such optical fibers is that they have good voltage isolation qualities and noise immunities. The present invention makes it possible to use low voltage electronic circuits to code information obtained by a sensing circuit and to transmit such information by optical fiber to a receiver circuit where the information is to be used. The use of electronic circuits of this type permits a reduction in the size of the sensing circuit and also permits the use of a shunt to sense the current and further permits the use of a conventional transformer to feed the supplies to the sensing circuit which is adapted at a location on the line.
Various types of sensing circuits have been used on high voltage lines to measure the current, but the majority of such apparatus or circuits utilize modulated coded signals or pulse width modulation.